The purpose of this study is to investigate the prevalence and incidence of Alzheimer's Disease and related disorders in an area of northern Manhattan from 155th Street to 181st Street. In this concentrated area, three major cultural groups - whites, blacks and Hispanics - are well represented. The investigators intend to estimate the numbers of prevalence cases and new incident cases. Subjects identified through one of the health network sites will be screened and referred to a memory disorder clinic for evaluation and treatment if there is evidence of dementia. The primary focus of the analysis will be on the prevalence and incidence of dementia in the community. The relative risk of dementia in this group will be examined using lifetime analyses, and this will be compared with a healthy, elderly comparison group.